Light emitting diode (LED) lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid state lighting (SSL) and have advantages over traditional lighting solutions such as incandescent and fluorescent lighting because they use less energy, are more durable, operate longer, can be combined in red-blue-green arrays that can be controlled to deliver virtually any color light, and generally contain no lead or mercury. In many applications, one or more LED dies (or chips) are mounted within an LED package or on an LED module, which may make up part of a lighting unit, lamp, “light bulb” or more simply a “bulb,” which includes one or more power supplies to power the LEDs. An LED bulb may be made with a form factor that allows it to replace a standard threaded incandescent bulb, or any of various types of fluorescent lamps. LEDs can also be used in place of florescent lights as backlights for displays.
For most LED lamps, LEDs may be selected to provide various light colors to combine to produce light output with a high color rendering index (CRI). The desired color mixing may be achieved, for example, using blue, green, amber, red and/or red-orange LED chips. One or more of the chips may be in a package with a phosphor or may otherwise have a locally applied phosphor. Due to variations in the light output and color reproduction of LED chips, LED lamps are typically individually calibrated at the time of production to take into account the specific LED chips' light output as a function of current, light color, and possibly other characteristics. Typically, LED lamps also include temperature monitoring, so that the LEDs' drive current can be automatically reduced in the case of overheating, and this temperature monitoring function must also be adjusted for the specific LED chips being used in a particular lamp. If the LED lamp supports external dimming, the dimming circuitry must take into account the color temperature changes at various current levels and corresponding light outputs in order to maintain a target color characteristic. The calibration adjustments necessary for each individual lamp ensure that the current output of the power supply under various conditions is appropriate for the specific LEDs used in each specific lamp.